Fragile X syndrome
Key points
- Fragile X syndrome is a genetic condition involving changes in the long arm of the X chromosome.
- Fragile X syndrome is the most common form of inherited mental retardation in males and a significant cause in females.
- Signs and tests A specific genetic test (PCR) can now be performed to diagnose this disease.
- There is no specific treatment for Fragile X syndrome.
Alternative names
Martin-Bell syndrome; Marker X syndrome
Definition
Fragile X syndrome is a genetic condition involving changes in the long arm of the X chromosome. It is characterized by mental retardation.
Causes, incidence, and risk factors
Fragile X syndrome is the most common form of inherited mental retardation in males and a significant cause in females. The inheritance is different from common dominant or recessive inheritance patterns. A fragile area on the X chromosome tends to repeat bits of the genetic code. The more repeats, the more likely there is to be a problem. Boys and girls can both be affected, but because boys have only one X chromosome, a single fragile X is more likely to affect them more severely.
Symptoms
- Family history of fragile X syndrome, especially a male relative
- Mental retardation
- Large testicles (macro-orchidism)
- Large size
- Tendency to avoid eye contact
- Hyperactive behavior
- Large forehead and/or ears with a prominent jaw
Signs and tests
A specific genetic test (PCR) can now be performed to diagnose this disease. This test looks for an expanded mutation (called a triplet repeat) in the FRAXA gene. Formerly a specific type of chromosome analysis was done and this may still be available.
There are very few outward signs of Fragile X syndrome in babies but one is a tendency to have large head circumference. Measurement of oversized testes in males can also suggest the diagnosis. An experienced geneticist may note subtle differences in facial characteristics. Mental retardation is the hallmark of this condition and, in females, this may be the only sign of the problem.
Treatment
There is no specific treatment for Fragile X syndrome. Instead, effort is directed toward training and education so that affected children can function at as high a level as is possible. Because the condition is not rare, specific educational approaches have been developed and tested.
Support Groups
National Fragile X Foundation
www.nfxf.org
800-688-8765
Expectations (prognosis)
The outcome depends on the extent of mental retardation.
Complications
Written and revised by
Andrey Nailor, M.D.
Our doctors write and review articles for accuracy and keep them up to date.
health.am provides general information, not medical advice. Always consult a qualified health professional about your own health.